Linux File System Hierarchy (FHS)

Important Directories

Directory	Purpose
/	Root directory, top of the filesystem
/bin	Essential user commands (ls, cp, mv, cat)
/sbin	System administration commands
/etc	Configuration files
/home	User home directories
/root	Root user's home directory
/var	Logs and frequently changing data
/tmp	Temporary files
/usr	User applications and utilities
/boot	Bootloader and kernel files
/dev	Device files
/proc	Process and kernel information
/sys	System hardware information
/opt	Optional third-party software
/mnt	Temporary mount points
/media	USB drives and removable media

Real-World Troubleshooting Scenario

Scenario: Disk Space Suddenly Full

User Complaint

Website is slow and application logs are not being generated.

---

Investigation

Step 1: Check Disk Usage

df -h

Output

Filesystem      Size  Used Avail Use%
/dev/xvda1       20G   20G    0G 100%

---

Step 2: Find Large Directories

du -sh /* 2>/dev/null

Output:

12G /var
2G  /usr
1G  /home

/var is consuming most space.

---

Step 3: Inspect Log Directory

cd /var/log
du -sh *

Output:

10G nginx

Nginx logs are filling the disk.

---

Fix

Compress or remove old logs:

sudo rm old-access.log
sudo rm old-error.log

Or rotate logs:

sudo logrotate -f /etc/logrotate.conf

---

Verify

df -h

Output:

Filesystem      Size  Used Avail Use%
/dev/xvda1       20G   10G   10G 50%

Disk space recovered.

---

Commands Practiced

pwd
ls
cd
df -h
du -sh
find

---

What I Learned Today

✅ Linux starts from the root directory (/)

✅ Every directory has a specific purpose

✅ Logs are usually stored in /var/log

✅ Configuration files are stored in /etc

✅ User data is stored in /home

✅ Disk-space issues can often be traced using:

• df -h

• du -sh

• find